Switch for optical signals

ABSTRACT

The invention relates to a switch ( 112 ) for optical signals and which has a number of outputs at least equal to the number of inputs and include means whereby an input signal is routed to at least one of those outputs. Each input receives information modulating optical carriers at different wavelengths. The switch ( 112 ) includes means ( 126   11   , 126   12   , . . . , 126   NB ) for grouping all the carriers received into non-contiguous subsets of carriers (G 11 , . . . , G 1B , . . . , G N1 , . . . , G NB ) and means ( 129   1   , 129   2   , . . . , 129   NB ) for selecting blocks of carriers from the same subset of carriers. The information corresponding to each subset of optical carriers is thus routed in blocks to the same subset output.  
     Switching the carriers at the subset level improves the quality of the output signal and limits the number of components for the same total quantity of information switched.

[0001] The invention relates to a switch for optical signals and moreparticularly to a switch for packet signals.

[0002] Telecommunications are expanding considerably. More and moreusers (individuals and businesses) are transmitting an increasing numberof messages in telecommunication networks. Also, the messages include anever-increasing quantity of information, for example when sendingpictures. To respond to this growing demand for information bit rate,telecommunications network operators are using optical signaltransmission, which modulates optical signals, generally produced bylasers, in accordance with the information to be transmitted, afterwhich the modulated signals propagate in a network of conductors oroptical fibers.

[0003] Transmitting signals optically has several advantages. Inparticular, the attenuation of the signal during transmission is lessthan in the case of electrical signals and the bandwidth of opticalfibers is greater. It is therefore possible to transmit several carrierswith different wavelengths simultaneously in the same fiber. Thistechnique, known as wavelength division multiplexing, achievesinformation bit rates of the order of 1 terabit/s.

[0004] In parallel with wavelength division multiplexing, time divisionmultiplexing enables simultaneous transmission of several calls on thesame carrier. In packet mode, each carrier transmits packets relating todifferent messages whose information has been divided up into packets,each packet being launched into the network with a header indicating itsdestination. When the packet passes through a switching device, thedevice dedicates resources to routing the packet during the time periodneeded to switch the packet to a requested output. Those resources arethen freed again for switching another packet. Because the packets areof limited duration, of the order of 1 microsecond, many calls can betransmitted in a short time period. This routing policy is currentlyused on the largest of all networks: the Internet.

[0005] Implementing switches using optical technology has beenenvisaged. Two types of switch can be distinguished:

[0006] cross-connect switches that set up semi-permanent connectionsbetween trunks routing a large number of multiplexed messages or calls,and

[0007] switches capable of routing calls or messages individually, i.e.that can be reconfigured for each new call or each new message.

[0008] The document JINNO M ET AL.: “ULTRA-WIDE-BAND WDM NETWORKS ANDSUPPORTING TECHNOLOGIES” CORE NETWORKS AND NETWORK MANAGEMENT,AMSTERDAM: IOS PRESS, NL, 1999, pages 90-97, XP000829416ISBN/90-5199-497-4 describes a cross-connect switch that receives andswitches, without demultiplexing them, optical signals consisting of 16carriers having different wavelengths. This switch cannot routeindividual calls or messages. Also, it is designed for very lowswitching speeds.

[0009] The invention relates to switches whose function is to routecalls or messages individually. Also, if the signals are transmitted inpacket mode, the switch must route all the packets present at therespective inputs to designated outputs and then change configuration toroute subsequent packets.

[0010]FIG. 1 is a block diagram of a prior art switch 10 that implementsthe above function. It has N inputs 10 ₁, 10 ₂, . . . 10 _(N) each ofwhich is adapted to be connected to a respective optical fiber 12 ₁ 12₂, . . . , 12 _(N). Each fiber transmits m channels consisting of mrespective carriers at different wavelengths λ₁, λ₂, . . . , λ_(m)modulated by pulses and by packets.

[0011] Each input 10 ₁, 10 ₂, . . . 10 _(N) is connected to a respectivecorresponding optical demultiplexer 13 ₁, . . . , 13 _(N) whichseparates the m carriers received at that input. Each carrier is thentransmitted to a wavelength converter and regenerator device 18 ₁, . . ., 18 _(N). The converted signals are recombined by an opticalmultiplexer 14 ₁, . . . , 14 _(N). N signals G₁, G₂, . . . , G_(N) areobtained at the output of these multiplexers. The N signals are thenbroadcast in m.N directions by respective couplers 15 ₁, . . . , 15_(N). They are then routed to m×N respective outputs 20 ₁, 20 ₂, . . . ,20 _(mN) of the switch 10 by m×N respective selector units 22 ₁, 22 ₂, .. . , 22 _(mN). Each selector unit is in two parts, namely, for the unit22 ₁, for example, an input selector first device 24 ₁ and a wavelengthselector second device 24 ₂.

[0012] For example, the input selector device 24 ₁ has N inputs each ofwhich is connected to respective outputs 16 ₁ to 16 _(N) of theconverter and regenerator devices 14 ₁, 14 ₂, . . . 14 _(N). The inputselector device 24 ₁ selects at most one of the N received signals G₁,G₂, . . . , G_(N). The selected signal is then routed to the wavelengthselector device 24 ₂. From the m carriers of the signal selected, thelatter device selects one carrier to be transmitted to an output 20 ₁ ofthe switch 10. The signals supplied at the outputs 20 ₁, 20 ₂, . . . ,20 _(mN) are then grouped into groups of m signals having differentwavelengths λ₁, λ₂, . . . , λ_(m) by multiplexers 14 ₁, . . . , 14 _(N)so that they can be transmitted via optical fibers 13 ₁, . . . , 13_(N).

[0013] In other embodiments, the number of output fibers and the numberof channels per output fiber can be different from N and m,respectively. On the other hand, the total number m.N of output channelsis equal to the total number of input channels.

[0014] Each input selector device 24 ₁, etc. includes at least Nselector units, for example optical amplifiers used as optical gates.Each wavelength selector device 24 ₂, etc. includes at least m selectorunits consisting of optical amplifiers used as optical gates, forexample, and wavelength-selective means. The switch 10 thereforeincludes at least m.N.(m+N) optical amplifiers. This large number ofcomponents is not favorable to reliability, simplicity or optimumfabrication cost. Also, each signal G₁, G₂, . . . , G_(N) is broadcastto an input of each of the m.N input selector units 22 ₁, 22 ₂, . . . ,22 _(mN). A consequence of this is that the power of each signal G_(i)is divided by a factor m.N.

[0015] Furthermore, after the selection effected by the first device 24₁, the selection operated by the second device 24 ₂ further divides thepower of the signal by a factor equal at most to a value from N to m.Accordingly, in total, the power of each input signal is attenuated byat least a factor N.m.max(N,m). This reduction in the power of thesignals in the selector device produces a low signal/noise ratio andtherefore distortion, which becomes problematic for signals at very highbit rates, for example bit rates higher than 10 Gbit/s.

[0016] An object of the invention is to reduce significantly the numberof times each signal is divided for the same total bit rate processed inthis kind of switch. This increases the signal/noise ratio and higherinformation bit rates can therefore be achieved.

[0017] The invention provides a switch for optical signals, the switchincluding a number of outputs at least equal to the number N of inputs,for routing an input signal to at least one output, each input beingadapted to receive signals modulating optical carriers having mdifferent wavelengths, characterized in that it includes:

[0018] means for grouping all of the carriers received at an input ofthe switch into non-contiguous subsets of carriers;

[0019] selector units for routing in blocks the signals corresponding toeach subset of optical carriers; and

[0020] means for dividing each subset and then transmitting all thecarriers of that subset to the same output of the switch.

[0021] The above switch processes a whole subset of the set ofwavelengths, i.e. a plurality of wavelengths, simultaneously, enablingthe same single component to be used for each function, such asamplification and switching, instead of one component for eachwavelength, and this applies up to the destination output. Accordingly,the signals are divided less than in the conventional optical switchshown in FIG. 1.

[0022] In the prior art switch, the factor by which the power of eachcarrier is divided is m×N before the input selector device 24 ₁. Betweenthe input selector device 24 ₁ and a wavelength selector second device24 ₂, the division factor is whichever is the greater of m and N. Theembodiments of the invention show that in the switch according to theinvention the division factor is reduced to N×B before the inputselector stage and to B between the input selector stage and the stagefor selecting the subset of wavelengths, B being the total number ofsubsets of carriers per optical fiber. For example, if the set ofcarriers comprises 16 carriers (m=16), and if each subset includes fourcarriers (B=4), the factor by which each signal is divided will be lessthan in the prior art switch shown in FIG. 1 by the following amount:$\frac{m \cdot {{Max}\left( {N,m} \right)}}{B^{2}} = {\frac{16 \times 4}{4 \times 4} = 4}$

[0023] One particular embodiment of the switch according to theinvention is characterized in that it further includes:

[0024] means for grouping all the subsets of carriers intonon-contiguous groups of subsets;

[0025] means for routing in blocks the information corresponding to aplurality of subsets of carriers; and

[0026] means for selecting a single subset of carriers per output of theswitch.

[0027] The above switch processes a plurality of subsets of carriers atthe same time, enabling the same single component to be used for eachfunction, such as amplification and switching, instead of one componentfor each subset.

[0028] Other features and advantages of the invention will becomeapparent in the course of the following description of embodiments ofthe invention, which description is given with reference to theaccompanying drawings, in which:

[0029]FIG. 1, already described, is a block diagram of a prior artoptical switch.

[0030]FIG. 2 is a block diagram of a first embodiment of an opticalswitch according to the invention, using subsets of carriers.

[0031]FIG. 3 is a block diagram of a second embodiment of an opticalswitch according to the invention, using groups of subsets of carriers.

[0032]FIGS. 4, 5, 10, 11, 12, 13 are block diagrams of variousembodiments of switching means that can be used in the secondembodiment.

[0033] FIGS. 6 to 9 are block diagrams of different variants of oneportion of the embodiment shown in FIG. 5.

[0034]FIG. 2 is a block diagram of a first embodiment of a switch 112 inaccordance with the invention. It has N inputs each connected to anoptical fiber 110 ₁, 110 ₂, . . . , 110 _(N) transmitting wavelengthdivision multiplexed signals. Each optical fiber transports m carrierswith different wavelengths λ₁, λ₂, . . . , λ_(m). Each carriertransports a series of messages, each message having a differentdestination. The switch must therefore be configured differently foreach message. There are two techniques which can be used to groupcarriers in the same subset of carriers:

[0035] grouping different messages having the same destination, or

[0036] grouping message segments within the same message.

[0037] It is also possible to combine the above two techniques. To bemore precise, the second technique entails dividing each message into aplurality of parts, each of which parts is transmitted by a carrier at adifferent wavelength from those of the other carriers transmitting theother parts of the message. The carriers being transmittedsimultaneously to the same destination, they form within each opticalfiber a subset of carriers to be routed to the same output.

[0038] In the embodiment shown in FIG. 2, all the optical fiberstransmit exactly the same number m of carriers and the messages havealready been divided upstream of the switch, i.e. in the network. Adifferent embodiment could include a time-division demultiplexer at theinput of the switch to distribute a message at bit rate D across fcarriers having different wavelengths and each having a bit rate D/f,with a time-division multiplexer at the output of the switch toreconstitute the message on a single carrier at bit rate D.

[0039] For example, for the m carriers arriving via the fiber 110 ₁, theswitch 112 uses B subsets of carriers S₁₁, . . . , S_(1B). For the mcarriers arriving via the fiber 110 _(N), the switch 112 uses B subsetsof carriers S_(N1), . . . , S_(NB). In this example, all subsetscomprise m/B signals with m/B respective different wavelengths λ₁, λ₂, .. . , λ_(m/B).

[0040] Each input of the switch 112 is connected to a respectivesynchronization device 114 ₁, 114 ₂, . . . , 114 _(N) whose function isto synchronize all packets transported by the carriers arriving at thatinput with a clock (not shown) of the switch, in order for the whole ofthe switch to function synchronously. The output of each synchronizationdevice 114 ₁, 114 ₂, . . . , 114 _(N) is connected to the input of acorresponding optical demultiplexer 115 ₁, 115 ₂, . . . , 115 _(N), forexample using an interference filter, for separating the m carriersreceived at each input, restoring them at m respective outputs. Those mcarriers are then grouped into B subsets S1 ₁, . . . , SN_(B) eachconsisting of m/B carriers.

[0041] Each subset S1 ₁, . . . , SN_(B) of carriers is transmitted to arespective wavelength converter and regenerator device 124 ₁, . . . ,124 _(NB). Each converter and regenerator device includes, for each ofm/B carriers it receives, a regenerator that amplifies and reshapes theoptical pulses of the signal. It further includes a wavelength converterthat changes the wavelength of the carrier.

[0042] For example, the converter and regenerator device 124 ₁ receivesm/B carriers with respective wavelengths λ₁, λ₂, . . . , λ_(m/B) andrestores m/B carriers with respective wavelengths λ′₁, λ′₂, . . . ,λ′_(m/B). The converter and regenerator device 124 _(B) receives m/Bcarriers with respective wavelengths λ_(m−(m/B)−1), . . . , λ_(m) andrestores m/B carriers with respective wavelengths λ′₁, λ′₂, . . . ,λ′_(m/B). Accordingly, the output wavelengths of all the wavelengthconverters of the converter and regenerator devices 124 ₁, . . . , 124_(NB) are exactly the same, for all the subsets of carriers S₁₁, . . . ,S_(1B).

[0043] Subsets of carriers having the same wavelengths λ′₁, . . . ,λ′_(m/B) are therefore obtained. This simplifies the fabrication of theoptical switch in accordance with the invention because the number ofwavelengths processed afterwards is reduced from m to m/B, for exampleenabling the use of amplifiers operating with a narrower wavelengthwindow than in the prior art switch. They are therefore less costly.

[0044] The carriers of the subsets S₁₁, . . . , S_(NB) obtained at theoutputs of the respective regenerator devices 124 ₁, . . . , 124 _(NB)are grouped by a respective multiplexer 126 ₁₁, . . . , 126 _(NB), eachof these multiplexers corresponding to one subset of carriers. Thus atthe output of the multiplexers 126 ₁₁, 126 ₁₂, . . . , 126 _(NB) a totalof N×B signals G₁₁, . . . , G_(1B), . . . , G_(N1), . . . , G_(NB) areobtained, each corresponding to one subset of carriers.

[0045] In this example, a subset of carriers transmits a message that isdivided into several parts, and each part of which is transmitted on onecarrier of the subset. The carriers relating to the same message aretherefore grouped into a single signal G_(ij). It is then possible toroute all the parts of the message to the same output fiber 146 ₁, . . ., or 146 _(N) by routing the signal G_(ij) to that fiber.

[0046] The signals G₁₁, . . . , G_(1B), . . . , G_(N1), . . . , G_(NB)from the multiplexers 126 ₁₁, 126 ₁₂, . . . , 126 _(NB) are amplified byerbium-doped fiber amplifiers 128. This type of amplifier has theadvantage of amplifying the signals with a signal/noise ratio and anoutput power much higher than those of semiconductor optical amplifiers.After they have been amplified by the amplifiers 128, the signals G₁₁, .. . , G_(1B), . . . , G_(N1), . . . , G_(NB) are broadcast by Nrespective broadcasters 115 ₁, . . . , 115 _(N) and then routed to theselector units 122 ₁, 122 ₂, . . . , 122 _(NB) by means of opticalfibers or optical conductors such as planar waveguides (to be moreprecise planar optical couplers).

[0047] Each selector unit 122 ₁, . . . , 122 _(NB) includes:

[0048] a respective switching device 129 ₁, . . . , 129 _(NB) whichselects one of the subsets of carriers from the N.B subsets broadcast bythe broadcasters 115 ₁, . . . , 115 _(NB); and

[0049] a demultiplexer 142 ₁, . . . , 142 _(NB) which separates the m/Bcarriers with wavelengths λ′₁, λ′₂, . . . , λ′_(m/B) of the respectivesubset 129 ₁, . . . , 129 _(NB) selected by the space switching device,and which applies those carriers to m/B respective converter andregenerator devices 145 ₁₁, . . . , 145 _(1m/B).

[0050] Each space switch device 129 _(i) includes:

[0051] A set of NB delay units 130 _(ij) for assigning to each signalreceived a time-delay that is a function of its priority. The priorityorder is included in the signal Gij itself, for example. The higher thepriority, the shorter the time-delay.

[0052] A set 132 _(i) of NB optical gates for choosing only one of thedelayed signals and therefore validating only one input of the spaceswitching device 129 _(i). The gates consist of semiconductor opticalamplifiers. A semiconductor optical amplifier, whether its gain isconstant or not, is activated when the signal that it receives must beselected for transmission. Only one gate is activated at a time. Notethat the delay units 130 _(ij) retain the signals that have not beenselected. In the absence of these delay units, the unselected signalswould be lost irrecoverably.

[0053] A switched amplifier device 134_(i) having NB inputs connected torespective outputs of the set of gates 132 _(i). Its role is to impartto the transmitted signal sufficient power at the stage of recombiningthe outputs of the various optical gates 132 _(i) in a way that avoidsaddition of optical noise from the amplifiers. The output of theamplifier device 134 _(i) constitutes an output 140 _(i) of the spaceswitching device 129 _(i).

[0054] Accordingly, compared to the prior art switch shown in FIG. 1,the total number of selection operations is reduced, since the number ofselector units 122 ₁, . . . , 122 _(NB) is N×B whereas in the prior artswitch the total number of selector units is N×m, B being a submultipleof m. In other words, processing the carriers of a subset at the sometime and transmitting them at the same time considerably simplifies theimplementation of the optical switch, can reduce the number ofcomponents, and improves signal processing quality.

[0055] The total number of selector units 122 ₁, 122 ₂, . . . , 122_(NB) is N.B and each selector unit 122 _(i) has N.B inputs. Each signalGij is applied to a corresponding input ij of each selector unit 122 ₁,122 ₂, . . . , 122 _(NB). Accordingly, the signal G₁₁ coming from anoutput of one of the amplifiers 128 is transmitted to the inputs indexed11 of the selector units 122 ₁, 122 ₂, . . . , 122 _(NB). Each input ofeach selector unit is associated with a delay unit 130 ₁₁, . . . , 130_(N) _(²) _(B) _(²) for assigning to each received signal a time-delaythat is a function of its priority. The priority order is included inthe signal Gij itself, for example. The higher the priority the shorterthe time-delay.

[0056] The demultiplexer 142 _(i) therefore supplies at m/B outputs thecarriers of a subset of carriers whose wavelengths are respectively λ′₁to λ′_(m/B). Then, each carrier is processed individually by arespective wavelength converter and regenerator device 145 ₁₁, 145 ₁₂, .. . , 145 _(Nm) implementing functions similar to those of a converterand regenerator device 124 ₁, . . . , 124 _(NB). Each includes aconverter for modifying the wavelengths of the carriers so that mcarriers with different wavelengths λ₁, λ₂, . . . , λ_(m) can betransmitted in the same fiber.

[0057] A respective multiplexer 150 ₁, 150 ₂, . . . 150 _(N) combines mcarriers with wavelengths λ₁, λ₂, . . . λ_(m) provided by B selectorunits 122, so that each output fiber 146 ₁ to 146 _(N) actuallytransmits the m carriers on the m input wavelengths. Note that thenumber of output wavelengths is generally equal to the number of inputwavelengths and that each wavelength λ_(i) received at the input appearsat the output. However, it is possible to choose output wavelengthvalues that are different from the input wavelength values.

[0058]FIG. 3 is a block diagram of a second embodiment 212 using N′groups of B′ subsets of B carriers. For example, the switch 212 groupsthe m carriers arriving via the input fiber 110 ₁ into B subsets S₁₁, .. . , S_(1B) each comprising m/B carriers. Each groups the m carriersarriving via the input fiber 110 _(N) into B subsets S_(N1), . . . ,S_(NB). All the subsets comprise m/B signals having m/B respectivedifferent wavelengths λ₁, λ₂, . . . , λ_(m/B).

[0059] The switch 212 then groups these NB subsets into N′ groups eachincluding B′ subsets of carriers. For example, in the embodiment shownin FIG. 3, N′=N and B′=B. The group SG₁ therefore includes the subsetsS₁₁, . . . , S_(1B). The group SG_(N) includes the subsets S_(N1), . . ., S_(NB).

[0060] Components that are similar to those of the switch 112 carry thesame reference numbers. The switch 212 has:

[0061] N inputs each connected to an optical fiber 110 ₁, 110 ₂, . . . ,110 _(N) transmitting wavelength division multiplexed signals;

[0062] N synchronization devices 114 ₁, 114 ₂, . . . , 114 _(N)analogous to those of the switch 112 (FIG. 2);

[0063] N wavelength converter and regenerator devices 124 ₁, . . . , 124_(NB) analogous to those of the switch 112 (FIG. 2);

[0064] N multiplexer devices 226 ₁, . . . , 226 _(N);

[0065] N optical amplifiers 228;

[0066] N broadcasters 215 ₁, . . . , 215 _(N);

[0067] N selector units 222 ₁, . . . , 222 _(NB);

[0068] N.m wavelength converter and regenerator devices 145 ₁, . . . ,145 _(Nm) analogous to those of the switch 112 (FIG. 2);

[0069] N optical multiplexers 150 ₁, . . . , 150 _(N) analogous to thoseof the switch 112 (FIG. 2); and

[0070] N outputs each connected to an optical fiber 146 ₁, 146 ₂, . . ., 146 _(N) transmitting wavelength division multiplexed signals.

[0071] Each selector unit 222 ₁, . . . , 222 _(NB) has:

[0072] N inputs connected to N respective outputs of N amplifiers 228supplying N respective signals H₁, . . . , H_(N); and

[0073] m/B outputs connected to m/B respective inputs of one of thewavelength converter and regenerator devices 145 ₁₁, . . . , 145 _(Nm).

[0074] This embodiment differs from the first one in that the broadcaststage includes N multiplexers 226 ₁, 226 ₁, . . . , 226 _(N) with minputs and N amplifiers 228 instead of N.B multiplexers 126 ₁, . . . ,126N with m/B inputs and N.B amplifiers 128. However, additionally, theNB selector units 222 ₁, . . . , 222 _(NB) are different because theyare optimized to exploit further the fact that the subsets of carriersare grouped together. Each selector unit 222 ₁, . . . , 222 _(NB) canselect a plurality of subsets of carriers simultaneously, and not onlyone subset, as in the switch 112.

[0075]FIG. 4 is a block diagram of a first embodiment 222 _(1a) of theselector unit 222 ₁ taken by way of example, for N=N′=16. It includes:

[0076] N optical gates 41 ₁, . . . 41 _(N), connecting N respectiveinputs of the unit 222_(1a) to a coupler 42 having N inputs and oneoutput;

[0077] an optical erbium-doped fiber optical amplifier 43 having aninput connected to the output of the coupler 42;

[0078] a demultiplexer 44 having an input connected to the output of theamplifier 43 and having N outputs;

[0079] m optical gates 45 ₁, . . . , 45 _(m) connected to respectiveoutputs of the demultiplexer 44; and

[0080] m/B multiplexers 46 ₁, . . . , 46 _(m/B) each with B inputs andone output, each input being connected to a respective output of thedemultiplexer 44 and the m/B outputs of the demultiplexers constitutingthe outputs of the selector unit 222 _(1a).

[0081] The gates 41 ₁, . . . , 41 _(N) are used to select a group ofsubsets of carriers from SG₁, . . . , SG_(N). In the example shown, N isequal to 16. The gates 451, . . . , 45N select m/B carriers and supplythem to the m/B respective multiplexers 461, . . . , 46m/B. The numberof inputs of each multiplexer 461, . . . , 46m/B is chosen to be equalto the number of carriers per subset (which is four, in the exampleshown in this figure).

[0082]FIG. 5 is a block diagram of a second embodiment 222 _(1b) of theselector unit 222 ₁ taken byway of example, for N=N′=16. It includes:

[0083] N optical gates 50 ₁, . . . , 50 _(N) divided into groups of N/p;each group of N/p gates connects N/p respective inputs of the unit 222_(1b) to a coupler 51 ₁, . . . , 51 _(p) having N/p inputs and oneoutput (the figure shows an example in which p=4 and N=16);

[0084] p optical gates 52 ₁, . . . , 52 _(p) having their inputsconnected to respective outputs of couplers 51 ₁, . . . , 51 _(p);

[0085] a coupler 53 having p inputs connected to respective outputs ofthe gates 52 ₁, . . . , 52 _(p) and having B outputs;

[0086] B optical gates 54 ₁, . . . , 54 _(B) having their inputsconnected to respective outputs of the coupler 53; and

[0087] a demultiplexer device 55 having B inputs connected to respectiveoutputs of the optical gates 54 ₁, . . . , 54 _(B) and having m/Boutputs constituting the outputs of the unit 222 _(1b).

[0088] This embodiment of the switch in accordance with the inventionrequires fewer optical gates than the prior art switch shown in FIG. 1.Each selector unit has N+2.B optical gates, i.e. a total of N.B.(N+2B)gates for the whole of the switch. Under these conditions, if N=16 andB=4, the total number of gates is 1 536. In a conventional switch, forwhich N=16 and m=16, the number of optical gates used for each selectorunit is m.N. (m+N)=8 192.

[0089] Accordingly, in this example, the number of optical amplifiers ofthe switch according to the invention is one fifth that of the prior artswitch, all other things being equal.

[0090] In the example shown in FIG. 5, N=16 and B=p=4. FIGS. 6 to 9 areblock diagrams of different embodiments of the demultiplexer device 55when m=16 and B=4.

[0091]FIG. 6 shows an embodiment 55 a including:

[0092] a first stage of B demultiplexers each having one input and m/Boutputs; and

[0093] a second stage of m/B couplers each having B inputs connected toa respective output of each of the demultiplexers of the first stage andhaving m/B outputs constituting the outputs of the device 55 a.

[0094]FIG. 7 shows an embodiment 55 b including:

[0095] a first stage of B demultiplexers each having one input and m/Boutputs; and

[0096] a second stage of m/B multiplexers each having B inputs connectedto a respective output of each of the demultiplexers of the first stageand having m/B outputs constituting the outputs of the device 55 b.

[0097]FIG. 8 shows an embodiment 55 c including:

[0098] if the subsets of carriers correspond to adjacent wavelengths:

[0099] a first stage consisting of a wavelength band multiplexer havingB inputs and one output; these inputs constitute the inputs of thedevice 55 c; and

[0100] a second stage consisting of a carrier interleaver having oneinput and m/B outputs, the inputs of this interleaver being connected torespective outputs of the first stage and its outputs constituting theoutputs of the device 55 c; or

[0101] if the subsets of carriers correspond to interleaved wavelengths:

[0102] a first stage consisting of a carrier interleaver having B inputsand one output; these inputs constitute the inputs of the device 55 c;and

[0103] a second stage consisting of a wavelength band multiplexer havingone input and m/B outputs, the inputs of this multiplexer beingconnected to the outputs of the first stage and its outputs constitutingthe outputs of the device 55 c.

[0104]FIG. 9 shows an embodiment 55 d including an array of waveguideshaving at least m waveguides in its internal structure. The array musthave at least B inputs and m/B outputs, m/B of those outputsconstituting the outputs of the device 55 c. Note that, depending on therespective arrangements of the inputs and outputs used, this device candemultiplex subsets of carriers corresponding to adjacent or interleavedwavelengths.

[0105]FIG. 10 is a block diagram of a third embodiment 222 _(1c) of theselector unit 221 ₁ considered by way of example. In this example, thenumber N of groups is equal to 8 and the number N′ of subsets per groupof subsets of carriers is equal to 2. The unit includes:

[0106] a space selector stage consisting of N optical gates 201 ₁, . . ., 201 _(N) divided into groups of N/p; the gates are connected to Nrespective inputs of the unit 222 _(1c);

[0107] p couplers 202 ₁, . . . , 202 _(p) each having N/p inputs and oneoutput; the inputs are connected to N/p respective outputs of a group ofoptical gates 201 ₁, . . . , 201 _(N) of the space selector stage;

[0108] a cyclic first array of waveguides 203 having q inputs, where qis greater than p; p of the q inputs of the array are connected to prespective outputs of the couplers 202 ₁, . . . , 202 _(p);

[0109] a carrier subset selector stage consisting of B optical gates 204₁, . . . , 204 _(B) having their inputs connected to B respectiveoutputs of the array 203;

[0110] m/B couplers 205 ₁, . . . , 205 _(p) each having B²/m inputs andone output, the B²/m inputs being connected to respective outputs of thearray of waveguides 203 via optical gates 204 _(i); and

[0111] a cyclic second array of waveguides 206 having m/B inputsconnected to m/B respective outputs of the couplers 205 ₁, . . . , 205_(m/B) and having m/B outputs constituting the outputs of the unit 222_(1c).

[0112] In the examples shown, N′=2, N=8, B′=2, B=4, p=4, q=5, m=8. Thenumbers m/B and q must be prime to each other. FIG. 10 shows how thisembodiment works in the case of routing a subset S₂₄ consisting of twocarriers λ₄ and λ₉ from eight carriers λ₁, λ₂, λ₃, λ₄, λ₆, λ₇, λ₈, λ₉arriving at the second optical gate 201 ₂. The references of thecarriers transmitted are indicated near the outputs of the components.The outputs of the array 203 can respectively restore the followingsubsets of carriers:

[0113] S₂₁: λ₁, λ₆

[0114] S₂₂: λ₂, λ₇

[0115] S₂₃: λ₃, λ₈

[0116] S₂₄: λ₄, λ₉

[0117] The subset of carriers λ₅, λ₁₀ is not included in this examplebecause it leads to an unused output of the array 203.

[0118] The outputs of the array 206 can respectively restore thefollowing carriers:

[0119] λ₂, λ₄, λ₆, λ₈, λ₁₀

[0120] λ₁, λ₃, λ₅, λ₇, λ₉

[0121] The gate 201 ₂ selects all the carriers λ₁, λ₂, λ₃, λ₄, λ₆, λ₇,λ₈, λ₉ arriving at that optical gate. It is controlled so that it allowsthose carriers to pass through it. The other gates 201 _(i) are shut.The array 203 restores only the carriers λ₄ and λ₉ at its outputconnected to the gate 204 _(B). The gate 204 _(B) is controlled to allowthose carriers to pass through it. The other gates 204 _(i) are shut.The coupler 205 _(m) transmits the carriers λ₄, λ₉ together to the array206. That array demultiplexes them and restores them on two separateoutputs.

[0122]FIG. 11 shows the same embodiment as FIG. 10, but indicates how itworks in the case of routing other carriers, applied to the gate 202 ₃,grouped into subsets S₃₁, S₃₂, S₃₃, S₃₄, as follows:

[0123] S31: λ₂, λ₇

[0124] S32: λ₃, λ₈

[0125] S33: λ₄, λ₉

[0126] S34: λ₅, λ₁₀

[0127] The comb of carriers is shifted for each input port of the array203. Consequently, the comb of carriers arriving at the gate 201 ₃ isλ₂, λ₃, λ₄, λ₅, λ₇, λ₈, λ₉, λ₁₀. The subset of carriers λ₆, λ₁₁ is notincluded in this example because it leads to an unused output of thearray 203.

[0128] The gate 201 ₃, for example, selects all the carriers λ₂, λ₃, λ₄,λ₅, λ₇, λ₈, λ₉, λ₁₀ arriving at the optical gate 201 ₃. In this example,it is controlled so that it allows those carriers to pass through it.The other gates 201 _(i) are shut. In this example, the carriers λ₃ andλ₈ can be transmitted via the port of the array 203 that is connected tothat gate. The array 203 restores only the carriers λ₃ and λ₈ at itsoutput connected to the gate 204 ₂. The gate 204 ₂ is controlled so thatit allows those carrier to pass through it. The other gates 204 _(i) areshut. The coupler 205 ₁ transmits the carriers λ₃ and λ₈ together to thearray 206. That array demultiplexes them and restores them on twoseparate outputs.

[0129] This embodiment of the switch according to the invention requiresfewer optical gates than the prior art switch shown in FIG. 1. Eachselector unit includes N+B optical gates, i.e. a total of N.B.(N+B)gates for the whole switch. Under these conditions, if N=16 and B=4, thetotal number of gates is 1 280. In a conventional switch, for which N=16and m=16, the number of optical gates used for each selector unit is:

[0130] m.N.(m+N)=8 192.

[0131] Accordingly, in this example, the number of optical amplifiers ofthe switch according to the invention is less than one sixth of that inthe prior art switch, all other things being equal.

[0132]FIG. 12 is a block diagram of a fourth embodiment 222 _(1d) of theselector unit 222 ₁ considered by way of example, for N=16, B=16. Itincludes:

[0133] a space selector stage consisting of N optical gates 301 ₁ . . ., 301 _(N), divided into groups of N.B/q each corresponding to a comb ofwavelengths C₁, . . . , C_(q/B) (a group of subsets of carriers);

[0134] q/B couplers 302 ₁, . . . , 302 _(q/B) each having N.B/q inputsand B outputs, the inputs of each coupler being connected to the outputsof the optical gates 301 ₁, . . . , 301 _(N);

[0135] q optional optical filters 303 ₁, . . . , 303 _(q) connected to qrespective outputs of the couplers 302 ₁, . . . , 302 _(q/B);

[0136] a stage for selecting a subset of carriers, consisting of qoptical gates 304 ₁, . . . , 304 _(q) having inputs connected torespective outputs of the filters 303 ₁, . . . , 303 _(q); and

[0137] a demultiplexer 305 having q inputs connected to q respectiveoutputs of the gates 303 ₁, . . . , 303 _(q) and having at least m/Boutputs constituting the outputs of the selector unit 222 _(1d); q ischosen to be greater than m.

[0138] The demultiplexer 305 can be implemented with an array ofwaveguides or with an optical filter in a “modified Littman-Metcalf”configuration. The q band-pass optical filters 303 ₁, . . . , 303 _(q)increase the power provided by the optical amplifiers constituting thegates by eliminating carriers of no utility from the subsets ofwavelengths not required. Without these filters, the latter wouldconsume some of the available power.

[0139] In the preferred embodiment, shown in FIG. 12, the filters areband-pass filters and the bands can therefore be adjacent. Each comb ofwavelengths C₁, . . . , C_(q/B) is shifted relative to the next comb byfour wavelengths so that the array 305 routes the wavelengths of eachcomb correctly. The number q of inputs (and outputs) of the array 305 isequal to 16. Only m/B outputs are used to constitute the outputsconnected to wavelength converter and regenerator devices 306 ₁, . . . ,306 _(m/B). Thus q-(m/B) outputs of the array 305 are not used.

[0140] It is possible to use those outputs more completely, given thataccess to the array 305 is bidirectional. It is possible to use theunused outputs as inputs in this fourth embodiment and also in the thirdembodiment (FIGS. 10 and 11).

[0141] For example, FIG. 13 is a block diagram of a variant of thefourth embodiment of the selector unit 222 _(1d) for N=16, B=16. Thisvariant uses the same array 310 for two switching stages SS_(2h) andSS_(2h+1), the array being used bidirectionally. The switching stageSS_(2h) includes:

[0142] a spatial selector stage consisting of N optical gates 301′₁, . .. , 301′_(N) divided into groups of N.B/q gates each corresponding toone comb of wavelengths;

[0143] q/B couplers 302′₁, . . . , 302′_(q/B) each having N.B/q inputsand B outputs, the inputs of each coupler being connected to respectiveoutputs of a group of N.B/q optical gates 301′₁, . . . , 301′_(N);

[0144] q optional optical band-pass filters 303′₁, . . . , 303′_(q)connected to q respective outputs of the couplers 302′₁, . . . ,302′_(q/B);

[0145] a stage for selecting a subset of carriers, consisting of qoptical gates 304′₁, . . . , 304′_(q) having inputs connected torespective outputs of the filters 303′₁, . . . , 303′_(q); and

[0146] a demultiplexer consisting of an array of waveguides 310 havingq′ ports on the left-hand side, constituting:

[0147] q inputs connected to q respective outputs of the gates 303′₁, .. . , 303′_(q), and

[0148] q′-q outputs, of which m/B outputs constitute the outputs of thestage SS_(2h+1), and can be connected to wavelength converter andregenerator devices 306″₁, . . . , 306″_(m/B); q is chosen to be greaterthan m.

[0149] The switching stage SS_(2h+1) includes:

[0150] a space selector stage consisting of N optical gates 301″₁, . . ., 301″_(N) divided into groups of N.B/q gates each corresponding to onecomb of wavelengths;

[0151] q/B couplers 302″₁, . . . , 302″_(q/B) each having N.B/q inputsand B outputs, the inputs of each coupler being connected to respectiveoutputs of a group of N.B/q optical gates 301″₁, . . . , 301′_(N);

[0152] q optional optical band-pass filters 303″₁, . . . , 303″_(q)connected to q respective outputs of the couplers 302″₁, . . . ,302″_(q/B);

[0153] a stage for selecting a subset of carriers consisting of qoptical gates 304″₁, . . . , 304″_(q) having inputs connected torespective outputs of the filters 303″₁, . . . , 303″_(q); and

[0154] a demultiplexer consisting of the array of waveguides 310,crossed in the opposite direction, its right-hand side having q′ portsconstituting:

[0155] q inputs connected to q respective outputs of the gates 303′₁, .. . , 303′_(q), and

[0156] q′-q outputs of which m/B outputs constitute the outputs of thestage SS_(2h), and can be connected to wavelength converter andregenerator devices 306′₁, . . . , 306′_(m/B).

[0157] It will be evident to the skilled person how to modify the thirdembodiment shown in FIG. 10 in an analogous way to use the same array ofwaveguides for at least two separate switching stages.

[0158] One embodiment of the combs of wavelengths can includewavelengths distributed regularly; for example each subset includes fourcarriers with intervals all equal to 100 GHz. To reduce intermodulationphenomena due to non-linearities in the response of the amplifiers, itmay be advantageous to distribute the carriers in a less regular manner,for example with each subset including four carriers with intervals of100 GHz, 200 GHz and 100 GHz, two adjacent subsets being separated by100 GHz. In another example, each subset includes four carriers withintervals of 200 GHz, 100 GHz, 100 GHz and two adjacent subsets areseparated by 100 GHz.

1. A switch (112) for optical signals, the switch including a number ofoutputs at least equal to the number N of inputs, for routing an inputsignal to at least one output, each input being adapted to receivesignals modulating optical carriers having m different wavelengths (λ₁,λ₂, . . . , λ_(m)); characterized in that it includes: means (126₁₁, . .. , 126 _(NB); 226 ₁₁, . . . , 226 _(NB)) for grouping all of thecarriers received at an input of the switch into non-contiguous subsets(S₁₁, . . . , S_(1B)) of carriers; selector units (129 ₁, . . . 129_(NB); 229 ₁, . . . , 229 _(NB)) for routing in blocks (G₁₁, . . . ,G_(NB)) the signals corresponding to each subset of optical carriers;and means (142, 145, 150) for dividing each subset and then transmittingall the carriers of that subset to the same output of the switch.
 2. Aswitch according to claim 1, characterized in that it further includes:means (226 ₁, . . . , 226 _(N)) for grouping all the subsets (S₁₁, . . ., S_(1B)) of carriers into non-contiguous groups (SG₁, . . . , SG_(N))of subsets; means (229 ₁, . . . , 229 _(NB)) for routing in blocks (H₁,. . . , H_(N)) the information corresponding to a plurality of subsetsof carriers; and means (44, 45, 46; 54, 55; 206; 305; 310) for selectinga single subset of carriers per output of the switch.
 3. A switchaccording to claim 1, characterized in that it includes means (124 ₁, .. . , 124 _(B)) for converting the wavelengths of the carriers of eachsubset into predetermined wavelengths (λ′₁, . . . , λ′_(m/B)) in aspectral window substantially narrower than the window of the mwavelengths at the input of the switch, in order for the selector units(129 ₁, 129 ₂, . . . , 129 _(NB)) to process wavelengths over a spectralwindow smaller than the spectral window of the m wavelengths at theinput of the switch.
 4. A switch according to claim 3, characterized inthat it includes converter means after the selector units (129 ₁, 129 ₂,. . . , 129 _(NB)) for converting the wavelengths (λ′₁, λ′₂, . . . ,λ′_(m/B)) of the carriers of each subset (S₁₁, . . . , S_(NB)) selected.5. A switch according to claim 1, characterized in that it includes N.Bselector units (122 ₁, . . . , 122 _(NB)), where N is the number ofinputs of the switch and B is the number of subsets of carriers receivedat the same input, and in that each selector unit (122 ₁, . . . , 122_(NB)) includes N.B optical amplifiers (132 ₁, . . . , 132 _(NB)) eachassociated with a corresponding input of the selector unit, said opticalamplifier being activated to transmit the signal applied to its input.6. A switch according to claim 1, characterized in that it furtherincludes variable delay means (130 ₁₁, 130 ₁₂, . . . , 130 _(N) _(²)_(B) _(²) ) associated with each selector unit (129 ₁, 129 ₂, . . . ,129 _(NB)) and controlled so as to delay the signal (G₁₁, . . . ,G_(1B), . . . , G_(N1), . . . , G_(NB)) selected by said unit as afunction of the priority accorded to said signal.
 7. A switch accordingto claim 1, characterized in that it further includes amplifier means(128) on the input side of the selector units (129 ₁, 129 ₂, . . . , 129_(NB)) for amplifying the subsets of carriers.
 8. A switch according toclaim 2, characterized in that a selector unit (222 _(1a)) includes: Noptical gates (41 ₁, . . . , 41 _(N)) coupling N respective inputs ofthe selector unit to a coupler (42) having N inputs and one output; ademultiplexer (44) having an input coupled to the output of the coupler(42) and having N outputs; N optical gates (45 ₁, . . . , 45 _(m))coupled to respective outputs of the demultiplexer (44); and m/Bmultiplexers (46 ₁, . . . , 46 _(m/B)) each having B inputs and oneoutput, each input being connected to a respective output of thedemultiplexer (44), and the m/B outputs of said demultiplexersconstituting the outputs of the selector unit.
 9. A switch according toclaim 2, characterized in that a selector unit (222 _(1b)) includes: Noptical gates (50 ₁, . . . , 50 _(N)) divided into groups of N/p gates;each group of N/p gates is coupled to N/p respective inputs of theselector unit (221b); p couplers (51 ₁, . . . , 51 _(p)) each having N/pinputs coupled to N/p gates and having one output; p optical gates (52₁, . . . , 52 _(p)) having their inputs coupled to respective outputs ofthe couplers (51₁, . . . , 51 _(p)); a coupler (53) having p inputsconnected to respective outputs of the gates (52 ₁, . . . , 52 _(p)) andhaving B outputs; B optical gates (54 ₁, . . . , 54 _(B)) having theirinputs coupled to respective outputs of the couplers (53); and ademultiplexer device (55) having B inputs connected to respectiveoutputs of B optical gates (54 ₁, . . . , 54 _(B)) and having m/Boutputs coupled to the outputs of the selector unit (222 _(1b)).
 10. Aswitch according to claim 2, characterized in that a selector unit (222_(1c)) includes: a space selector stage including N optical gates (201₁, . . . , 201 _(N)) divided into groups of N/p gates, said gates beingcoupled to N respective inputs of the selector unit (222 _(1c)); pcouplers (202 ₁, . . . , 202 _(p)) each having N/p inputs and oneoutput, said inputs being coupled to N/p respective outputs of a groupof optical gates (201 ₁, . . . , 201 _(N)) of the space selector stage;a cyclic first array of waveguides (203) having q inputs, where q isgreater than p, p inputs of the q inputs of said array being coupled top respective outputs of the couplers (202 ₁, . . . , 202 _(p)); a stagefor selecting subsets of carriers including B optical gates (204 ₁, . .. , 204 _(B)) having their inputs connected to B respective outputs ofthe first array of waveguides (203); m/B couplers (205 ₁, . . . , 205_(p)) each having B²/m inputs and one output, said B²/m inputs beingcoupled to respective outputs of the first array of waveguides (203) viaoptical gates (204_(i)); and a cyclic second array of waveguides (206)having m/B inputs coupled to m/B respective outputs of the couplers (205₁, . . . , 205 _(m/B)) and having m/B outputs coupled to the outputs ofthe selector unit (222 _(1c)).
 11. A switch according to claim 2,characterized in that a selector unit (222 _(1d)) includes: a spaceselector stage including N optical gates (301 ₁, . . . , 301 _(N))divided into groups of N.B/q gates each corresponding to a comb ofwavelengths; q/B couplers (302 ₁, . . . , 302 _(q/B)) each having N.B/qinputs and B outputs, the inputs of each coupler being coupled to theoutputs of the optical gates (301 ₁, . . . , 301 _(N)) of the spaceselector stage; a stage for selecting a subset of carriers consisting ofq optical gates (304 ₁, . . . , 304 _(q)) having inputs connected torespective outputs of the couplers (302 ₁, . . . , 302 _(q/B)); and ademultiplexer (305) having q inputs connected to q respective outputs ofthe gates (303 ₁, . . . , 303 _(q)) of the stage for selecting a subsetof carriers and having at least m/B outputs coupled to the outputs ofthe selector unit (222 _(1d)), q being chosen to be greater than m. 12.A switch according to claim 11, characterized in that a selector unituses the same array (310) for two switching stages (SS_(2h), SS_(2h+1)),said array being used bidirectionally.
 13. A switch according to claim11, characterized in that a selector unit (222 _(1d)) further includes qoptical filters (303 ₁, . . . , 303 _(q)) coupling q respective outputsof the couplers (302 ₁, . . . , 302 _(q/B)) to the inputs of the qoptical gates (304 ₁, . . . , 304 _(q)) of the stage for selecting asubset of carriers.